It is well known that piezoelectric materials deform when subjected to electrical voltages. This deformation occurs in such a way that the dimensions of the piezoelectric material expand and contract when an alternating voltage is applied. The piezoelectric material behaves like an electrical capacitor and can be described by the typical equation for capacitance ##EQU1##
where c=capacitance
Q=electric Charge PA2 V=applied Voltage.
The piezoelectric material is connected to an electric supply by suitable connections. As a result of the relationship shown above, both the voltage and electric charge supplied must be sufficient to create high forces and deformations of the material. Since the voltage and charge are applied to the entire volume of the piezoelectric material, there is a corresponding deformation of the entire volume.
Loudspeakers employing a piezoelectric transducer capable of propagating surface acoustic waves to drive a diaphragm have been proposed as an alternative to moving coil loudspeakers. Such a device was described by Martin in U.S. Pat. No. 4,368,401 and later in Takaya in U.S. Pat. No. 4,439,640. Both inventions dealt with attaching a disc shaped piezoelectric element to a diaphragm. Martin's device used a thick glue layer (10 to 50% of the carrier plate thickness) between a carrier plate and the piezoelectric ceramic. The adhesive layer served to attenuate resonance. Any displacement in the piezoelectric material is directly related to the applied electrical potential.
In both the Martin and Takaya patents, and in other similar art relating to electrically driven piezoelectric materials, the piezoelectric materials are used to drive diaphragms that are essentially the same size, in terms of surface area, as the piezoelectric materials. Therefore, it would be very costly to utilize the concepts of such patents and similar prior art to drive large, i.e. "Extended" diaphragms, in that piezoelectric materials are very expensive and a large single piezoelectric element or many smaller piezoelectric elements would be needed to drive comparatively sized diaphragms. Therefore it would be advantageous if piezoelectric materials could be adapted to drive diaphragms that are much larger in size that such piezoelectric materials.